1. Field of the Invention
The invention relates to a control apparatus for a hybrid vehicle and, more particularly, to a control apparatus that detects degradation of an electrical storage apparatus mounted in a hybrid vehicle.
2. Description of Related Art
Hybrid vehicles that drive by drive force from an electric motor have a battery for storing electric power that is to be supplied to the electric motor. The battery capacity declines from full charge capacity of an initial state by various factors, including the current, voltage, temperature and SOC of the battery as well as the elapsed time, etc. . . . . In order to determine when to replace the battery due to degradation, it is necessary to precisely detect the decline in the full charge capacity.
Japanese Patent Application Publication No. 2000-224701 (JP 2000-224701 A) discloses a degradation determination apparatus for a battery that is mounted in a hybrid vehicle. The degradation determination apparatus integrates the output current of the battery and also the regenerative current stored into the battery during the period from when the battery charge is at an upper limit until when it reaches a lower limit. This degradation determination apparatus performs the determination regarding degradation of the battery by comparing the integrated value of current with a pre-set degradation criterion value (see (JP 2000-224701 A).
However, in the hybrid vehicles as described above, it is rare that the battery charge changes from the upper limit to the lower limit. Therefore, there is possibility that the occurrence frequency of performing the detection of degradation of the battery may become inconveniently low.